A method for assembling a sliding door fitting used for coupling an appliance door to a furniture door, which is coupled to a furniture body. The appliance is installed into the furniture body and an assembly aid tool is fixed to the device door. The appliance and furniture doors are closed so that markings are introduced onto an inner surface of the furniture door by pins of the assembly aid tool. The furniture door is opened and the assembly aid tool is released and removed. A base housing of the sliding door fitting is positioned using the markings. The base housing is secured to the furniture door and a slider of the sliding door fitting is fixed to the device door. The assembly aid tool has an angular shape with a first limb and a second limb. The first limb has at least one pin for introducing at least one marking onto the furniture door, and the second limb has a securing opening for fixing the assembly aid tool onto an end face of the device door.